Field of the Invention
The present invention relates to a position detection apparatus which detects a distance from an object to be measured.
Description of the Related Art
Japanese Patent Laid-open No. 2006-349606 discloses a gap sensor which measures a distance from an object to be measured by illuminating a light beam from an LED onto a reflection surface via a diffraction grating to receive reflected light on a light receiving element. The gap sensor disclosed in Japanese Patent Laid-open No. 2006-349606 uses fringes of a light intensity distributions that are formed by incoherent light transmitting through two diffraction gratings. By detecting a gap amount based on phase variations of the fringes of the light intensity distribution, it is possible to perform stable gap detection without depending on a light emitting amount of a light source.
Japanese Patent Laid-open No. 2005-326232 discloses a photoelectric encoder that uses a Doppler shift of light scattered by movement of a moving grating to calculate a displacement of the moving grating.
However, in a gap detection method disclosed in each of Japanese Patent Laid-open No. 2006-349606 and Japanese Patent Laid-open No. 2005-326232, there is a possibility that an error occurs in a detection value due to an inclination of the reflection surface, and thus it is difficult to perform gap detection (position detection) with high accuracy.